Ruby dup/clone recursively

Question

I have a hash like:

h = {'name' => 'sayuj', 
     'age' => 22, 
     'project' => {'project_name' => 'abc', 
                   'duration' => 'prq'}}

I need a dup of this hash, the change should not affect the original hash.

When I try,

d = h.dup # or d = h.clone
d['name'] = 'sayuj1'
d['project']['duration'] = 'xyz'

p d #=> {"name"=>"sayuj1", "project"=>{"duration"=>"xyz", "project_name"=>"abc"}, "age"=>22}
p h #=> {"name"=>"sayuj", "project"=>{"duration"=>"xyz", "project_name"=>"abc"}, "age"=>22}

Here you can see the project['duration'] is changed in the original hash because project is another hash object.

I want the hash to be duped or cloned recursively. How can I achieve this?

Sergio Tulentsev · Accepted Answer · 2012-01-03T10:20:43.580

40

Here's how you make deep copies in Ruby

d = Marshal.load( Marshal.dump(h) )

edited Jan 03 '12 at 10:20

answered Jan 03 '12 at 10:13

Sergio Tulentsev

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This creates full copies of all objects referenced by `h`. This might be exactly what is needed by Sayuj for simple String hashes. With more complex objects, this might not be desired anymore. Once could override the `Hash#dup` method to dup all hashes in `values` recursively. But that would need to be extended for every object type. – Holger Just Jan 03 '12 at 10:21
2

@HolgerJust: yes, that's why it's called a "deep copy" :-) – Sergio Tulentsev Jan 03 '12 at 10:22
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Of course. I just wanted to mention that it might do more than the OP intended (although it's probably just fine) :) So it's just for, well, future reference. – Holger Just Jan 03 '12 at 10:25
2

Note that this will not work when there is a default proc (e.g. `h = Hash.new {|h,k| h[k] = 1}`) – Mark Thomas Jan 03 '12 at 12:44

score 3 · Answer 2 · answered Nov 23 '15 at 11:22

3

If you are in Rails: Hash.deep_dup

answered Nov 23 '15 at 11:22

fguillen

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Малъ Скрылевъ · Answer 3 · 2014-09-29T13:01:41.953

2

In case the Marchal #dump/load pair isn't work, for rails there is a Hash's method #deep_dup, so you can:

h = {'name' => 'sayuj', 
 'age' => 22, 
 'project' => {'project_name' => 'abc', 
               'duration' => 'prq'}}

h1 = h.deep_dup

edited Sep 29 '14 at 13:01

answered May 15 '14 at 12:48

Малъ Скрылевъ

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the method should be h.deep_dup instead of h.deep.dup – yopefonic Sep 27 '14 at 02:50
1

`deep_dup` method will turn a Class into anonymous Class, not recommended. – Tian Chen Apr 25 '17 at 15:54
@TianChen example? – Малъ Скрылевъ May 03 '17 at 15:17
1

see this example: `class Abc; end` `h = { 'class' => Abc }` `h1 = h.deep_dup # => => {"class"=>#}` – Tian Chen May 18 '17 at 03:34

score 1 · Answer 4 · edited Nov 09 '15 at 22:28

This is an answer to a reasonably old question, but I happened upon it while implementing something similar, thought I'd chime in for a more efficient method.

For the simple, two level deep hash like above, you can also do something like this:

d = h.inject({}) {|copy, (key, value)| 
    copy[key] = value.dup rescue value; copy
}

I ran a test on a hash of hashes with 4k elements, each a few hundred bytes, and it was about 50% faster than the Marshal.dump/load

Of course, it's not as complete, as it won't work if you have a hash as, e.g., the value of the 'project_name' field, but for a simple 2 level hash, it works great / faster.

score 0 · Answer 5 · answered Jan 31 '18 at 16:29

Another alternative is to use the full_dup gem (full disclosure: I am the author of that gem) that handles arrays, hashes, structs, and is extendable to user defined classes.

To use:

require 'full_dup'
# Other code omitted ...
d = h.full_dup

Also note that full_dup handles complex data relationships including those with loops or recursion.

Ruby dup/clone recursively

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